1. Field of the Invention
The present invention generally relates to a tape cassette of the type used for electromagnetically recording digital signals on magnetic tape and, more particularly, to protecting such magnetic tape from contaminants which may enter the cassette and compromise tape performance.
2. Description of the Prior Art
It is well known in the prior art to record analog signals on magnetic tape housed in a cassette which is insertable into a conventional recording/playback apparatus having a magnetic head which reads the analog signals and converts the same into sound and/or video output signals. It is also well known to record digital signals on so-called "floppy discs" having an opening which is accessed by the magnetic head. Although generally satisfactory for their intended purpose, there are problems associated with the use of floppy discs. For example, a user, through inadvertence, inexperience or deliberate action, may roughly handle the disc and touch the playing surfaces of the disc through the aforementioned access opening. The user may thus leave his fingerprints, outlined by oil, grease and water deposits, on the playing surfaces. Dust, dirt and other contaminants may enter via the access opening to adhere to the playing surfaces of the disc and, of course, such contaminants are particularly attracted to the fingerprint-marked areas. Such contaminants, of course, compromise tape performance. In addition, the non-rigid nature of the highly flexible floppy discs renders their handling much more difficult and awkward, as compared to rigid discs.
In an attempt to resolve the problems associated with floppy discs, the prior art has recently proposed using a magnetic tape cassette of the type exemplified in FIGS. 4-7 for recording digital signals. This prior art cassette comprises an upper rectangular casing 1 and a lower rectangular casing 2, each molded of a synthetic resin plastic material, and both joined together to form a cassette housing having an open front side. A magnetic tape 3 is mounted in the interior of the housing for travel between a pair of rotary reels 4, 5. The magnetic tape 3 is wound around the reel 4 and is sequentially advanced past a guide roller 6, a tape pad 7, another guide roller 8, and the other reel 5 in conventional manner. The tape 3 is advanced in a taut state past the open front side of the cassette housing during recording/playback operation.
It is also known to provide a protective cover 9 for covering the length of the magnetic tape 3 which is located at the front side of the cassette housing. The cover 9 is pivotably mounted on the housing for movement between an exposed position in which the cover 9 is remote from the tape at the front side of the housing, to a covered position in which the cover 9 overlies the tape at the front side of the housing. In the covered position, the cover 9 prevents dust, dirt and other contaminants, as well as the user's fingers, from entering the open front side of the housing and contacting the magnetic tape thereat. The aforementioned contaminant problem is very acute in the case of recording digital signals because the digital signals are recorded on much smaller lengths of the tape, as compared to recording analog signals. Put another way, the density of the digital signal is higher than that for the analog signal.
As shown in the enlarged views of FIGS. 6 and 7, the protective cover 9, which advantageously is made of a suitable resin material, has an elongated planar main portion extending along the length of the open front side of the housing, and a pair of arm portions 91 and 92 at opposite end regions of the main portion and extending perpendicularly thereof. A pair of stub shafts 93, 94 are connected on the arm portions and are colinearly arranged along a pivot axis around which the cover 9 pivots in either circumferential direction. The shafts 93, 94 are inserted into triangular bearing holes 10 which are formed in opposite side wall portions 101, 201 of the upper and lower casings 1 and 2, respectively. Each bearing hole 10 is formed by combining a pair of notches 102, 202 which are formed in abutting edges of the side wall portions 101, 201.
As shown in the covered position illustrated in FIG. 4, the conventional protective cover 9 covers a taut length of the magnetic tape 3 at the open front side of the cassette housing to close the cassette when the same is not in use. Consequently, there is no danger that the user's fingers and/or contaminants will contact the magnetic tape 3 and compromise the integrity and true reproduceability of the recorded digital signals. When the cassette is to be used, the protective cover 9 is first pivoted about the pivot axis to either the upper covered position shown in FIG.5 in which the main portion of the cover is located above the upper casing 1, or the lower covered position in which the main portion of the cover is located below the lower casing 2. Once the cover 9 is moved away from its overlying position with respect to the tape 3, then the cassette can be inserted into any recording/playback apparatus.
For the sake of completeness, it is noted that each of the reference numerals 11, 12 designates a tape end detecting hole into which is inserted a light-emitting element or a light-receiving element of the tape recording/playback apparatus. Each of the reference numerals 13, 14 designates a hole into which is inserted a capstan drive of the apparatus. The numeral 15 designates a shield plate.
Although the above described cassette with its protective cover has proven to be generally satisfactory for its intended purpose of protecting the tape at the front side of the housing from being contacted by finger and/or contaminants, the contaminant problem still remains. More particularly, experience has shown that, over the course of time, powder is produced and deposited on the tape within the cassette housing, thereby compromising tape performance. The powder is produced during the pivoting of the cover 9 among its various positions. The outer surfaces of the stub shafts 93 and 94 frictionally engage and, over time, grind down the inner surfaces of the bearing holes 10, thereby producing a ground powdery substance of synthetic resin material. The bearing holes 10, which extend through the side wall portions 101 and 201, serve as passages along which the thus-produced powder may enter the interior of the housing. The contaminant-entry problem is aggravated by the fact that the stub shafts 93, 94 are inserted from the exterior of the cassette housing through the side wall portions 101, 201 into the interior of the housing. The thus-introduced powder eventually deposits onto the magnetic tape and mars subsequent tape performance.